Hydroprocessing can include processes which convert hydrocarbons in the presence of hydroprocessing catalyst and hydrogen to more valuable products. Hydrocracking is a hydroprocessing process in which hydrocarbons crack in the presence of hydrogen and hydrocracking catalyst to lower molecular weight hydrocarbons. Depending on the desired output, a hydrocracking unit may contain one or more beds of the same or different catalyst. Hydrocracking can be performed with one or two hydrocracking reactor stages.
A hydroprocessing recovery section typically includes a series of separators in a separation section to separate gases from liquid materials and cool and depressurize liquid streams to prepare them for fractionation into products. Hydrogen gas is recovered for recycle to the hydroprocessing unit. A typical hydrocracking recovery section comprises six columns. A stripping column strips hydrogen sulfide off of a liquid hydrocracked stream with a steam stream. A liquid stripping stream is fractionated in a deethanizer column whose overhead is sponged along with a vapor stripping overhead stream in an absorber column to product LPG. A product fractionation column separates the stripped liquid hydrocracked stream into an overhead fractionated stream comprising naphtha, perhaps a distillate side product stream and a bottoms stream comprising unconverted oil comprising distillate. The product fractionation overhead stream and the deethanizer column bottoms stream are fractionated in a debutanizer fractionation column into a debutanizer overhead stream comprising LPG and a debutanized bottoms stream comprising naphtha. The debutanized bottoms stream is fractionated in a naphtha splitter column into a light naphtha overhead stream and a heavy naphtha bottom stream.
Hydroprocessing recovery sections comprising fractionation columns rely on external utilities that originate from outside of the hydroprocessing unit to provide heater duty to vaporize the fractionation materials. Fractionation sections that rely more on heat generated in the hydroprocessing unit than external utilities are more energy efficient. Stripping columns typically rely on steam stripping to separate volatile materials from heavier hydrocarbon materials.
In some regions, diesel demand is lower than demand for lighter fuel products. Distillate or diesel hydrocracking is proposed for producing the lighter fuel products such as naphtha and liquefied petroleum gas (LPG). The naphtha product stream may be proposed for a petrochemical production and taken as feed to a reformer unit followed by an aromatics complex.
There is a continuing need, therefore, for improving the efficiency of processes for recovering petrochemical feedstock from hydrocracked distillate stocks.